1. Field of the Invention
The present invention relates to a method of and an apparatus for measuring irregularities of road surface and, more particularly, to a method of and an apparatus for measuring irregularities of road surface by a cooperation between a beam signal transmitting portion for applying a spot of a laser beam onto the road surface and a beam signal receiving portion for receiving the laser beam reflected by the road surface.
2. Description of the Prior Art
A method for measuring irregularities of a road surface has been known in which a spot of a laser beam is applied to the road surface and the reflected laser beam is received by a photo-sensor which produces a signal indicating the height of irregularity, e.g., a convexity or concavity, whereby information concerning the irregularity is obtained.
This known method, however, suffers from a problem in that the center of the laser beam spot is not always located correctly, due to variation in the state of the road surface such as color, gradient and degree of wetness of the road surface, with the result that the quality of the information concerning the irregularity is impaired to cause an error in the measurement.
The known measuring method making use of a laser beam usually employs an image processing system which processes the detection signal into image signals so as to visualize the road irregularity information thereby facilitating the examination of the state of the road surface. In consequence, the scale of the measuring apparatus becomes so large that the apparatus cannot have a wide adaptability.
Also known is a mechanical-type apparatus for measuring irregularity of the road surface. This apparatus has a sensor portion 100 which includes a shaft 102 adapted to be moved up and down in accordance with vertical displacement of a roller 101 which follows any irregularity of a road surface A, a rack 103 fixed to the shaft 102, a pinion 104 meshing with the rack 103 and an encoder 105 adapted to be rotated by the pinion 104. Thus, the irregularity of the road surface is converted into a vertical movement of the shaft 102 and the rack 103 and is further converted into rotational displacement in the encoder 105 through the engagement between the rack 103 and the pinion 104. The encoder 105 produces pulses of a number corresponding to the rotational displacement, and the number of the pulses is counted by a pulse counter the output of which is delivered to a height calculating circuit 107 which calculates the height of the irregularity thereby producing irregularity information.
This mechanical-type measuring apparatus, however, is disadvantageous in that the reliability is impractically low due to the fact that the path of transmission of measured value involves may movable mechanical parts. In addition, the measuring accuracy is largely affected by the diameter of the roller, particularly when the surface of a long road is measured continuously. For instance, a too small diameter of the roller will hamper the measurement because such a small roller cannot roll onto any step which may exist on the road surface. Conversely, a too large roller diameter will impair the accuracy of the measured data because such a large roller cannot well respond to small recess which may exist in the road surface, as shown in FIG. 2.